1. Field of the Invention
The present invention relates to an apparatus for transporting a ribbon from a payout reel to a takeup reel. It particularly relates to a ribbon transport apparatus wherein tension is maintained in all or some of the ribbon intermediate between the takeup spool and the payout spool. It yet further relates to ribbon transport mechanisms comprising only one motive actuator.
The invention is hereinafter described with reference to the transporting of an ink ribbon in a printing apparatus for the presentation of a fresh portion of ribbon to an impact printing apparatus after the printing of each character. The invention is not limited to such an application and may equally be applied to transport apparatus for magnetic tape in audio, digital and video applications and to transport apparatus for reeled paper. The invention may thus be applied to any apparatus wherein a ribbon of any kind of material is paid out from one reel and taken up onto another reel.
2. The Prior Art
In an ink ribbon transport system, an ink ribbon is drawn from a payout reel and taken up by a takeup reel. Between the payout reel and the takeup reel, there is provided a printing station whereat an impact printer using dot matrix or a solid typeface strikes the ribbon against a paper sheet to leave an imprinted visible character. The ink ribbon is moved on by one character space after the imprinting of each character for a fresh portion of the inked ribbon to be presented to the paper for the next character to be printed. The inked ribbon intermediate between the payout reel and the takeup reel is maintained in a state of tension so that it may be moved between the reels with a certainty of presenting fresh ribbon to the print head on each occasion.
Various systems exist for moving the ribbon between the reels. In a first system, the takeup reel is urged to take up the ribbon by a constantly-rotating friction clutch, whilst the payout reel is urged to oppose paying out by a constantly-rotating friction clutch driven by a motor in the opposite direction to the direction of motion of the payout reel when it is, in fact, paying out. Intermediate between the payout reel and the takeup reel there is provided a pinch wheel and capstan assembly for moving the ribbon. Such a system is to be found in most domestic cassette recorders where a single motor drives the pinch wheel and capstan assembly, the friction clutch on the takeup reel and the friction cluch on the payout reel. In more expensive magnetic cassette systems a separate motor can be provided for each of these functions. If tension is not maintained in the intermediate tape, then uncertainty of tape movement and starting and stopping can ensue. Such systems may be taken as typical prior art with regard to the present invention when it is used with magnetic tape.
For the transport of ink ribbons, it has been the practice to provide, on the paying out reel, a friction clutch which moves to oppose the paying out of the ink ribbon on each occasion of advancing of the ink ribbon. This system has the disadvantage of long-term instability on the opposing torque from the driven friction clutch and of a lack of tensioning drive to the clutch when the ink ribbon is not being moved. In an alternative improvement to such a system, a dedicated motor can be constantly run to drive the friction clutch on the payout reel. This system meets the objections to the earlier ink ribbon system in that the constantly-driven friction clutch on the payout reel takes up any slack tape intermediate between the two reels and maintains tension in the static tape. The improvement in function is achieved at the considerable expense of an additional motor over and above the required to advance the ink ribbon.
It is therefore desirable to provide a ribbon transport system utilizing only a single motor to advance the ribbon where tension is maintained in the ribbon between reels when the ribbon is moving, and where any slack ribbon between the reels is taken up when the ribbon is not being transported and where tension is maintained in the ribbon intermediate and stationary between the reels.
When the reels on a tape transport mechanism are large, the rotational inertia of each reel is correspondingly large. High reel inertia causes two problems. Firstly, when the ribbon or tape first begins to be drawn from the payout reel, tension in the ribbon or tape coming from the payout reel can momentarily reach very high levels as the payout reel is caused to accelerate to the necessary angular velocity. The high tension in the tape or ribbon so induced is undesirable on the ground that it may cause stretching and breakage of the tape or ribbon.
The second problem caused by high reel inertia happens when it is desired to stop the payout reel. A payout reel of high inertia will continue to run on and payout ribbon or tape as it decelerates to rest. The presence of excess slack ribbon or tape in the transport apparatus caused by this running on is undesirable.
It further becomes desirable to provide a tape transport apparatus where the payout reel may be steadily and progressively accelerated without shock tension in the ribbon or tape pulling on the payout reel, and wherein the payout reel may rapidly be brought to a halt when tape drawn therefrom ceases to pull on the payout reel.